1. Field of the Invention
The present invention is generally related to a multi-functional pH meter and fabrication thereof, and more particularly to a multi-functional pH meter and fabrication thereof by integrating semiconductor processes and embedded system technology.
2. Description of the Prior Art
Ion sensitive field effect transistors (ISFETs) are micro sensing devices appeared in 70s and quickly developed. For only 30 years till now, there are more than 600 research papers and 150 other related papers, such as enzyme field effect transistors (EnFETs) and immuno field effect transistors (IMFETs) (P. Bergveld, “Thirty years of ISFETOLOGY: What happened in the past 30 years and what may happen in the next 30 years”, Sensors and Actuators B, Vol. 88, pp. 1-20, 2003.). In addition, ion sensitive field effect transistors can be used to measure pH values and ion concentrations, such as Na+, K+, Cl−, NH4+, Ca2+, in stead of fragile glass electrodes (Miao Yuqing, Guan Jianguo, and Chen Jianrong, “Ion sensitive field effect transducer-based biosensors”, Biotechnology Advances, Vol. 21, pp. 527-534, 2003.). The idea was first introduced by P. Bergveld. By using a metal oxide semiconductor field effect transistor (MOSFET) without a gate electrode, a device with a SiO2 layer is placed in aqueous solution together with a reference electrode. The electric current passing the device changes with the hydrogen-ion concentration, whose response is similar to that of a glass electrode. Thus, it has the acid-base sensing characteristic (Chen Jian-pin, Lee Yang-li, Kao Hung, “Ion sensitive field effect transistors and applications thereof”, Analytical Chemistry, Vol. 23, No. 7, pp. 842-849, 1995; Wu Shih-hsiang, Yu Chun, Wang Kuei-hua, “Measurement by chemical sensors”, Sensor technology, No. 3, pp. 57-62, 1990).
Some ISFET sensing devices have been commercialized, such as ISFET pH meters made by Arrow Scientific, Deltatrak, and Metropolis. However, it has problems of stability and lifetime, for example drift phenomena and hysteresis effect. The present invention discloses another type of ISFETs, an extended gate field effect transistor (EGFET). The field effect transistor (FET) is isolated from the chemical measurement environment. The chemical sensing film is deposited on one end of the signal wire extended from the area of the gate electrode. The portions of the electric effect and the chemical effect are packaged separately. Therefore, compared to conventional ISFETs, EGFETs are easy in packaging and storage and have better stability (Liao Han-chou, “Novel calibration and compensation technique of circuit for biosensors”, June, 2004, Department of electrical engineering, Chung Yuan Christian University, Master dissertation, pp. 11-29).
Recently, there are many researches in characteristics of the extended gate ion sensitive field effect transistors, such as device design (Li Te Yin, Jung Chuan Chou, Wen Yaw Chung, Tai Ping Sun, and Shen Kan Hsiung, “Separate structure extended gate H+-ion sensitive filed effect transistor on a glass substrate”, Sensors and Actuators B, Vol. 71, 106-111, 2000; Li Te Yin, Jung Chuan Chou, Wen Yaw Chung, Tai Ping Sun, and Shen Kan Hsiung, “Study of indium tin oxide thin film for separative extended gate ISFET”, Materials Chemistry and Physics, Vol. 70, pp. 12-16, 2001; Li Te Yin, Jung Chuan Chou, Wen Yaw Chung, Tai Ping Sun, Kuang Pin Hsiung, and Shen Kan Hsiung, “Study on glucose ENFET doped with MnO2 powder”, Sensors and Actuators B, Vol. 76, pp. 187-192, 2001; Yin Li-Te, “Study of Biosensors Based on an Ion Sensitive Field Effect Transistor”, June, 2001, Department of biomedical engineering, Chung Yuan Christian University, Ph. D. dissertation, pp. 76-108.), characteristic analysis (Jia Yong-Long, “Study of the extended gate field effect transistor (EGFET) and signal processing IC using the CMOS technology”, June, 2001, Department of electrical engineering, Chung Yuan Christian University, Ph. D. dissertation, pp. 36-44; Chen Jia-Chi, “Study of the disposable urea sensor and the pre-amplifier”, June, 2002, Department of biomedical engineering, Chung Yuan Christian University, Master dissertation, pp. 51-80; Jia Chyi Chen, Jung Chuan Chou, Tai Ping Sun, and Shen Kan Hsiung, “Portable urea biosensor based on the extended-gate field effect transistor”, Sensors and Actuators B, Vol. 91, pp. 180-186, 2003; Chung We Pan, Jung Chuan Chou, I Kone Kao, Tai Ping Sun, and Shen Kan Hsiung, “Using polypyrrole as the contrast pH detector to fabricate a whole solid-state pH sensing device”, IEEE Sensors Journal, Vol. 3, pp. 164-170, 2003; Jui Fu Cheng, Jung Chuan Chou, Tai Ping Sun, and Shen Kan Hsiung, “Study on the chloride ion selective electrode based on the SnO2/ITO glass”, Proceedings of The 2003 Electron Devices and Materials Symposium (EDMS), National Taiwan Ocean University, Keelung, Taiwan, R.O.C., pp. 557-560, 2003; Jui Fu Cheng, Jung Chuan Chou, Tai Ping Sun, and Shen Kan Hsiung, “Study on the chloride ion selective electrode based on the SnO2/ITO glass and double-layer sensor structure”, Proceedings of The 10th International Meeting on Chemical Sensors, Tsukuba International Congress Center, Tsukuba, Japan, pp. 720-721, 2004.), characteristics of drift phenomena and hysteresis effect (Liao Han-chou, “Novel calibration and compensation technique of circuit for biosensors”, Master dissertation, Department of electrical engineering, Chung Yuan Christian University, pp. 11-29, June, 2004; Chu Neng Tsai, Jung Chuan Chou, Tai Ping Sun, and Shen Kan Hsiung, “Study on the hysteresis of the metal oxide pH electrode”, Proceedings of The 10th International Meeting on Chemical Sensors, Tsukuba International Congress Center, Tsukuba, Japan, pp. 586-587, 2004; Chu Neng Tsai, Jung Chuan Chou, Tai Ping Sun, and Shen Kan Hsiung, “Study on the sensing characteristics and hysteresis effect of the tin oxide pH electrode”, Sensors and Actuators B, Vol. 108, pp. 877-882, 2005.).